In a system disclosed in Patent Document 1, for example, a DPF (Diesel Particulate Filter) for capturing particulate matter in an exhaust gas (hereinafter, also referred to as “PM”) is disposed in the exhaust passage of the internal-combustion engine. Disposed downstream of the DPF is a PM sensor for detecting the amount of PM which was not captured by the DPF and allowed to pass therethrough.
The PM sensor of Patent Document 1 includes an insulating layer allowing the adhesion of PM and electrodes disposed on the insulating layer and spaced from each other. When the PM sensor is exposed to the exhaust gas so that the PM in the exhaust gas is deposited between the electrodes, conductivity between the electrodes varies according to the deposition amount of PM and hence, inter-electrode resistance varies. According to Patent Document 1, the PM amount in the exhaust gas related with the amount of inter-electrode PM deposition is detected by detecting the resistance value of the PM sensor. Hence, a malfunction of DPF or the like is detected based on the resistance value of the PM sensor.
By the way, when the amount of inter-electrode PM deposition exceeds a given value, the inter-electrode resistance does not vary any more, which disables the subsequent output of a value corresponding to a PM deposition amount. According to a technique of Patent Document 1, on the other hand, at a point in time when the amount of inter-electrode PM deposition is increased to some degree, PM reset is performed by heating an element part of the PM sensor by means of a built-in heater for a predetermined length of time so as to combustively remove the deposited PM.